This invention relates to a process for production of alkyl or substituted alkyl p-dimethylaminobenzoates and in particular, though not exclusively to the production of ethyl p-dimethylaminobenzoate.
Alkyl p-dimethylaminobenzoates have previously been made by the reductive alkylation of alkyl p-aminobenzoates using formaldehyde in the presence of hydrogen and a catalyst, for example palladium on charcoal, under forcing conditions of temperature and pressure.
The reaction is a complex multi-stage mechanism, proceeding through reduction of intermediate Schiff's bases (formaldehyde-amine condensation products) and is difficult to take to completion even under the forcing conditions of temperature and pressure used. As a result, impurities from unreacted Schiff's bases and side reactions can typically be present in the product at up to 2% in total.
The alkyl p-dimethylaminobenzoates thus produced are used as photoinitiators in wide range of applications and the presence of such impurities may, in certain of these applications, adversely affect the photoinitiation properties. Also, the impurities may themselves be toxic or react during the photoinitiation process to produce side products that are toxic.
Removal of the impurities present in the alkyl p-dimethylaminobenzoates produced by the known process would add significantly to production costs.
It is an object of the present invention to provide a process for the production of alkyl or substituted alkyl p-dimethylaminobenzoates which mitigates the above-discussed problems of the known process.